Grid for fluorescent lamp units

ABSTRACT

A plastic moulded grid for lamp units for ceiling or wall illumination comprising a system of equally spaced tubular bodies, which are bodies of revolution or have a cross-section formed as a planar or spherical polygon, the bodies further having outer convex and inner concave reflecting faces, the reflection preferably being obtained by means of metallizing these faces which are of single or double curvature and have a generant curve with a constant or increasing radius in a direction away from a light source, the center of curvature of the generant curve is placed on the side facing the interior of the tubular body and the curve is preferably of the form y y . xn. The smallest inner cross-sectional area of the tubular bodies are nearest to the light source. The grid is constructed in such a way that the incident light rays are transmitted both through and between the tubular bodies, the grid producing a pear-shaped light distribution curve in a polar coordinate system, which curve is symmetrical about the 0* axis and extends as a closed curve below the 90* axis and tangent thereto.

United States Patent [191 Willumsen Apr. 30, 1974 GRID FOR FLUORESCENT LAMP UNITS Poul Willumsen, Mortonsvej 1 1, 2800 Lyngby, Denmark [22] Filed: Jan. 2, 1973 [21] Appl. No.: 320,588

[76] Inventor:

[30] Foreign Application Priority Data Jan. 4, 1972 Denmark 27/72 [52] US. Cl. 240/78 LD, 52/473, 52/506, 52/633, 161/41, 161/139 [51] Int. Cl. F2lv 11/00 [58] Field of Search 240/78 R, 78 LD, 78 LK,

[56] References Cited UNITED STATES PATENTS 3,600,570 8/1971 Okada 240/78 LD 2,839,671 6/1958 Cullen 240/78 CK X 3,246,138 4/1966 Florence 240/78 R X 3,708,381 l/1973 Schwartz 240/78 LD X 2,937,265 5/1960 Blitzer 240/78 LK X 3,124,310 3/1964 Lipscomb 240/78 LK Primary Examiner.loseph F. Peters, Jr. Attorney, Agent, or Firm-Eric H. Waters ABSTRACT A plastic moulded grid for lamp units for ceiling or wall illumination comprising a system of equally spaced tubular bodies, which are bodies of revolution or have a cross-section formed as a planar or spherical.

polygon, the bodies further having outer convex and inner concave reflecting faces, the reflection preferably being obtained by means of metallizing these faces which are of single or double curvature and have a generant curve with a constant or increasing radius in a direction away from a light source, the center of curvature of the generant curve is placed on the side facing the interiorof the tubular body and the curve is preferably of the form y y x". The smallest inner cross-sectional area of the tubular bodies are nearest to the light source. The grid is constructed in such a way that the incident light rays are transmitted both through and between the tubular bodies, the grid producing a pear-shaped light distribution curve in a polar coordinate system, which curve is symmetrical about the 0 axis and extends as a closed curve below the 90 axis and tangent thereto.

26 Claims, 11 Drawing Figures PATENTED APR 30 1914 SHEET 1 BF 9 PATENTEDAPRBO m4 3308.421 saw u M 9 Fly 6 PRIOR ART PATENTED man I914 3.808.421

' I SHEET 5 0F 9 Fig. 8

ATENWU (WK :3 "F f SHEET 7 [IF 9 PRIOR '1 GRID FOR FLUORESCENT LAMPUNITS The invention relates to a grid for fluorescent lamp units for ceiling or wall illumination.

It is known to provide a fluorescent lamp unit for use in a frame, comprising one or more light sources and a plurality of self-supporting reflector elements or grids. Such grids may have a directional effect, as is known in so-called low luminance grids which direct a controlled luminous flux down towards a region of limited illumination, or they may be formed as shielding grids producing a diffuse room illumination. In the socalled low luminance grids, all the vertical faces of the grid are formed as parabolic arches whereby the grid prevents the light sourcefrom being viewed directly,

and from the side the grid has'a dull greyish appearance. These low luminance grids transmit a controlled luminous flux, i.e. they illuminate only a limited space. The known shielding grids, which consist of a plurality of plane parallel vertical faces at right angles to one another, emit a diffuse luminous flux for illuminating a room, but in this grid it is possible to see the light source itself from certain angles.

It is an object of the present invention to provide a grid having the properties of both a low luminance grid anda shielding grid. By means of the grid according to the invention there is achieved a' controlled luminous flux directed against a primarily illuminated object as well as room illumination. A lamp provided with such a grid is capable of providing a bright illumination of objects below the lamp and at the same time have an accurately adjusted luminous power extending in all directions from which the lamp unit is normally viewed,

so that on the one hand there is no possibility of being dazzled by the lamp'while achieving on the other hand such a light effect as to be felt as an architecturally integrated part of the room in which it is located in that one has a clear impression of the origin of the light. A grid of this type is suitable both for ceiling and wall illumination unlike the heretofore known fluorescent lamp units.

The grid according to the invention for fluorescent lamp units for ceiling or wall illumination comprises a system of equidistant, open tubular elements having both external convex reflecting faces and internal concave reflecting faces, said faces being of single or double curvature and having a generant curve whose radius of curvature is preferably constant or increasing in a direction away from alight source, the center of curvature of the generant curve of both faces being in a direction toward the inner part of the tube, the end of the tubular element facing the light source having a smaller inner cross-sectional area, than the end turned away from the light source, the grid being constructed so that the incident luminous flux will be transmitted both through and in between the tubular elements. With such a grid the luminous flux from the light source will partly pass through the tubular elements, being directed down towards the object it is desired primarily to illuminate as a controlled luminous flux, and secondly a certain percentage of the luminous flux will pass the grid outside the tubular elements through the spaces therebetween, where the luminous flux will be reflectedagainst the external convex faces and leaveby the openings farthest away from thelight source as a diffuse luminous flux. Viewed from the side, the grid will give the impression of a number of dark regions obtained from the tubular elements which do not reflect any light to the sides, and a number of luminant faces obtained from the luminous flux diffusedly' reflected from the external faces.

The grid is further characterized in that the 'individ ual elements are bodies of revolution whose generant curves are essentially parabolic segments, and in that the generant curve of the external convex face may conform to the generant curve of the internal concave face, and'particularly by the element being a body of revolution whose rotary axis forms a given angle to the main axis of a curve of the shape y p x", of which the generant curve forms part thereof. The grid is specifically distinctive because the curve, part of which is the generant curve of the body of revolution is a second degree parabola. This has the advantage that the luminous'flux through the elements may be directed in a controlled manner, as it is possible to calculate mathematically or by trial and error to adjust the luminous flux through the elements.

It is yet another distinctive feature of the grid that the focal point of the generant curve is disposed at or adjacent the edge of the body of revolution closest to the light source. This ensures guidance of the luminous flux through the body. Furthermore, the-edge of the body farthest away from the light'source is fixed relative to the geometric height of the body by light rays originating from the edge closest to the light source and, having a given angle to the axis of the body, will specifically cut off the parabolic arches at their points farthest away from the light source. This has the advantage that the entireluminous flux which enters through theopening closest to the light source will flow out as controlled light through the opening farthest away from the light source at a desired angle.

A second embodiment of the grid according to the invention is characterized in that the cross section of the individual elements is formed as a planar or spherical polygen'with two sides, and in that the convex and concave faces of the elements have generant curves which are elliptical, hyperbolic or'parabolic segments, the generant curves of the faces being a second degree parabola. By varying the form of the individual elements it is possible to vary the volume of controlled luminous flux in relation to the volume of diffuse luminous flux reflected from the face of the grid farthest away from the light source.

The second embodiment is further characterized in that a focal line or focal point of a face is substantially at the edge of the element closest to the light source and opposite the respective face. This ensures positive guidance of theluminous flux from the light source into the element. g

The grid according to said second embodiment is further distinguished in that the edge of the element farthest away from the light source .is fixed relative to the geometric height of the element by light rays originating from the edge closest to the light source and, having an inclination of a given angle such as 45 to the grid, being specifically able to cut off the parabolic arches at their points farthest away from the light source. Thus the entire luminous flux entering the element will flow out as controlled luminous flux from the face of the grid farthest away from the light source.

The aforesaid grids are further distinguished in that the individual elements are moulded, bonded or otherwise mounted with respect to each other so as to form a connected assembly of a given design, as determined by the desired technical light effect. This has the advantage of rendering the volume of controlled light relative to the size of the element higher than the volume of passing diffuse light as the area of the spaces between the individual elements will be the smallest posible.

The grid is further characterized in that the individual elements are interconnected such that their geometric centers viewed from the. light source and also from the opposite side of the grid towards the light source will form a plane polygonal or spheric polygonal pattern. This ensures that the grid will havea design giving it an attractive appearance both when the illumination is on or when it is off which is essential for marketing purposes.

The grid is further distinguished in that the individual elements are moulded together or otherwisemounted in and interconnected by a shielding grid, known per se, having walls in plane parallel relationship and disposed at right angles, to one another. This feature makes it possible to control the ratio of the passing controlled luminous flux to the passing diffuse luminous flux.

The latter configuration is furthermore distinguished by the individual elements being inserted so as to have their rotary axis coincide withan X-portion removed 1 from the shielding grid, or by the individual elements being so inserted as to have their rotary axis coincide with the intersecting line'of the horizontal diagonals of the individual openings 'of Y the shielding grid. One achieves thereby 'a simple geometric pattern which is easy to construct. It is also an essential feature of the grid that theshielding grid is of lesser height than the individual elements. This ensures'that the shielding grid will not prevent any portion of the luminous flux from reaching the opening of the elements closest to the light source, and it is-also ensured that the highest possible percentage of the luminous flux from the light source will reach the shielding grid, and it has further been possible to reduce the'number of reflections prior to the diffuse luminous flux leaving the face of the grid farthest away from the light source.

The grid is also distinguished by being made from a material capable of being'formed into sheets, for example plastics. The material also may be glass or metal although this is not expedient as it will add too much weight to the grid. The use of plastics permits the grid to be made by a simple operation such as moulding.

Furthermore, the grid is distinguished by a reflecting coating consisting in metallizing the surface of the material, or in an inherently double-reflecting face coated with a transparent face coated with a transparent material on one or both sides. It is recommended in the preferred embodiment to metallize the surface of the material as this involves the least luminous loss.

It is, another feature of the grid that in the reflecting coating of certain faces such as all faces, except the internal sides of the element, a coloring matter may be added. This ensures that the controlled luminous flux transmitted from the light source towards the primarily illuminated object will be as high as possible, whereas the toning obtained by adding a coloring matter will dim the diffuseluminous flux slightly such that the diffuse luminous flux will not be felt as a cold reflected light but rather as a warm and pleasant room illumination.

The grid is also distinguished by a configuration permitting the light transmitted to spread as a controlled luminous flux like low luminance grids known per se, i.e. grids where the lateral face is substantially parabolic, and also to spread as a difiuse luminous-flux like the distribution of luminous flux 'in shielding grids known per se, i.e. grids where the lateral face has substantially plane parallel faces, and by having a light distribution curve basically as shown in FIG. 11 and further described below.

Finally, the grid is distinguished by a light distribution curve in a polar. coordinate system in symmetrical about the 0 axis, extending as a closed curve below the axis and with the latter as a horizontal tangent, and being otherwise a substantially pear-shaped curve having a marked indentation in the upper portion of the pear-shaped curve, which means that the pear-shaped curve has two deflection tangents on either side of the axis of symmetry in the upper portion of pear-shaped curve, or by the light distribution curve being shaped as a pear section having an enlarged extension of its stalk. This lightdistribution curve has not been disclosed in any heretofore known fluorescent lamp unit and must therefore be described as a novel surprising effect of the .grid according to the invention. This will also be evident if one studies British Zonal Classification described by the Illuminating Engineering Society in I.E.S. Technical Report No. 2: The Calculation of Utilisation Factor the B. Z. Method," London, revised edition, February 1971, whose light distribution curves for comparative measuring with other lamps are all of essentially pointed oval shape.

' The invention will now be explained below with reference to the drawings in which FIG. 1 illustrate a grid for fluorescent lamp units for ceiling illumination or as wall unit according to the invention, viewed in section along the line [-1 in FIG. 2,

FIG. 2 shows the grid in FIG. 1, viewed from the light source,

FIG. 3 is a second grid according to the invention, viewed in section along the line III-III in FIG. 4,

FIG. 4 shows the grid in'FIG. 3, viewed fromthelight source,

FIG. 5 shows the construction of a body of revolution for the lamp unit in FIG. 1, designated V, and the construction of the faces of FIG. 3.

FIG. 6 shows the light transmission through a parabola ,of revolution as used in the grid,

FIG.v 7 shows the light distribution of an unshielded fluorescent lamp,

FIG. 8 shows two light distribution curves of fluorescent lamp units where the grid consists of plane parallel facesoriented substantially away from the light source toward the object illuminated,

FIG. 9 shows a light distribution curve for a unit with I experiments at the Lighting Engineering Laboratory,

and

FIG. 11 shows alight distribution curve derived from experiments at the Lighting Engineering Laboratory having the characteristic configuration of the light distribution curve for the grid according to the invention.

FIGS. 1 and 2 show a grid 1 according to the invention where the numeral 2 designates bodies of revolution or elements having both external, convex reflecting faces 3 and internal, concave reflecting faces 4. The individual elements 2 are secured to or moulded integrally with a shielding grid which consists of a plurality of walls 6, 7 at right angles to one another. As will be evident from FIG. 2, every second wall 6, 7 is continuous and every second wall 6, 7 interrupted'by elements 2. All faces of walls 6, 7 are reflecting. The walls 6', 7 are shorter in length that the elements 2, extending from the edge B farthest away from the light source 5. The elements 2 may also be mounted within the rectangular squares of the shielding body withthe rotary axis of the elements coinciding with the intersection of diagonals such as in a chessboard pattern. If necessary, the shielding grid may be left out altogether, and the individual elements may be joined and secured at the edge B farthest away from the light source 5. I

The elements 2 are bodies of revolution having a generant curve whose radius of curvature increases in a direction away from the light source 5 and with the center of curvature of their generant curve in a direction toward the interior of the tube. The generant curve of the configuration specifically shown here are parabolic segments of a second degree parabola. The generant curve and the construction of theelements will be further described below. i

FIG. 3 and 4 show a second embodiment of the grid according to the invention. In this case the grid 1 is composed of a plurality of elements 2' having a square cross section and being interconnected at the edge farthest away from the light source. However, it is possible to use other plane polygons or spherical polygons as well for creating the cross-sectional pattem..The faces 3, 4' of the elements 2 are reflecting and of single curvature in the example shown, having a generant curve whose radius of curvature is increasing in a direction away from the light source 5 and with the center of curvature of the generant curve in a direction toward the interior of the tube. The generant curves of the embodiment shown here are parabolic'segments of a second degree parabola. It is noted that adjoining comers of the individual faces 3', 4' resemble in shape hiproofs of arched configuration. In the construction shown in FIGS. 3 and 4 the aforesaid shielding grid is left out as in each individual square the external convex faces of the individual elements form a shielding grid section of substantially the same technical light effect as a corresponding square in a shielding grid of conventional construction.

The structures illustrated here are moulded from plastics in large or small sections and thereafter assembled and bonded together. The finished grid is then metallized on all faces with a highly reflecting material such as aluminum, whereupon, if desired, the grid is immersed into a suitable pickle bath to render the reflecting face resistant to corrosion, etc-Another method consists in constructing the grid from reflecting faces and coating these with a transparent material such as a clear plastic material. The latter method will, however, result in a somewhat more'costly and heavier unit and therefore is not preferred. v

To dim or tone the luminous flux in between the elements 2, 2', the spaces 8, 8' between the elements may be covered with a transparent sheet of a material such as plastic or glass to which a coloring matter has been added. An alternative procedure for dimming the luminous flux between the elements comprises adding to the metallizing coat for the external faces 3, 3 of the elements a coloring matter'and also to the plan parallel walls 6, 7 at right-angles to one another.

FIG. 5 shows the construction of the generant curve of the faces 3, 4 and 3' and 4'. A parabola P of the configuration y p x is drawn in conventional manner. Through the focal point B, of the parabola there is drawn a line at the angle V to the main axis, which line intersects the parabola P at B The center normal C of B, and B is drawn, and the parabolic segment 8 D, is reflected with the center normal C as axis of symmetry on to B,D,. The edge closest to the light source 5, 5 is determined by the line B,B while the edge farthest away from the light source 5, 5 may be determined by drawing lines from B, and B of the angle V to the'center normal. The point where these intersect the original parabola and the reflected parabola respectively will determine the edge farthest away from the light source 5, 5'. If bodies of revolution are desired, the center normal C is used as theaxisof rotation. In the case of other cross sections of the element 5, thecurve is displaced in space along the desired curve.

The passage of light through an optical system having internal parabolic faces will be further explained with reference to FIG. 6. I I

FIG. 6 illustrates an optical system having the characteristic that light hitting the upper surface of the system at any angle of incidence will be able to'leave the lower surface of the system at an angle to a vertical line which is always less or equal to V. i

The system consists of opposing reflecting faces whose vertical sectional lines form parabolas P, and P These parabolas are symmetrical about the vertical axis of the system as explained above. In a rotary symmetrical system it is possible to have the parabolas cover each other.

The parabola P, has the focal point B and the axis A, forming the angle V to the vertical axis.

The parabola P being symmetrical to P, is so positioned as to pass through the focal point B, of the parabola P,. For reasons of symmetry thefoacl' point B, of the parabola P must'therefore be on the parabola P,.

Only that part of the parabola P shown in solid lines in the figure and which is between the foacl point B, and the intersection of line L which is designed to pass through the focal point B of P and forms the angle V to the vertical axis, is used. I l

The corresponding section of P, is used. The systems functions as follows:

An imaginary light source is placed at the focal point B,'. The rays from this light source hitting the opening B of the system will readily be seen to leave the system in directions forming an angle to thevertical axis which is less than V. All rays from B, hitting the parabola P, will be reflected in a direction forming the angle V to the vertical axis. Rays from B, hitting the parabola P,

will likewise by necessity be reflected in directions forming small angles to the vertical axis.

If the light source is located on the line between B, and B it will be seen that only the ray hitting the parabola P, in B will be reflected at the angleV. All other rays will be transmitted at other angles.

The same applies to light sources located above the line B,-B and it follows that no ray could leave the system in directions forming an angle to the vertical axis greater than V.

plained above.

The Lighting Engineering Laboratory, the Technical University of Denmark, the Technical High School of Denmark has measured the photometric characteristics of the optical grid according to the invention. The principle of measuring'is further described in the publication Lampetten" No. 4/1967 issued by the Lighting Engineering Society, Denmark on pages 79 to 88. The principle of the method of measuring depends on using a special photocell of at least the same size as the lamp and which is designed so as to be sensitive onlyto light hitting the surface thereof atright angles, which will, among other things, makeit possible to reduce the distance from the lamp to the measuring photocell.

A photocell being only sensitive to incident light at right angles will measure the true luminous-power of the lamp, provided the photocell is of at least the same sideof which is a grid permitting passageway light hitting the grid within a very small angle to the normal.

' The light penetrating the grid into the cavity is reflected by the white faces thereof, summated and measured by a photomultiplier. To ensure that the light will hit the'photocell substantially at'right angles thereto, a special guiding raster is used, comprising eight layers, each about 1 cm deep andeach provided with a hole onthe surface facing the light source. The openings are centered with respect to each other so as to guide a light ray from the lamp toward the photocell]. The measuring itself is effected by the photocell being rotated 36 about the centrally positioned lamp. It should be mentioned that the Commision International d Eclarage comite E-2.2. Photometric Requirements for Luminaries have accepted the measuring principle.

In testing the grid according to the invention, the grid was positioned such that its plane formed an angle of 45 to the photocell, and the transmission factor and light distribution curve of the grid were measured.

Prior to measuring the light distribution of the grid, comparative tests were made to show the light distribution ofthe incident flux on the grid. For evaluating the invention, FIGS. 7, 8 and 9 show light distribution curves for a fluorescent lamp without mounting unit and also for ordinary heretofore used fluorescent lamp units. FIGS. 7 to 9 have been reproduced from Lys og Belysning (Lighting and Illumination) Nos. 3, 4 and 5, published by Aschehoug Dansk Forlag", Copenhagen 1967/1968, respectively pages 3-29, 5-25 and 4-10. It will be evident from FIGS. 8 and 9 that the light distribution curves of the heretofore customary fluorescent lamp units are substantially con vex.

In comparing these curves with the light distribution curve of FIG. 11, the grid according to the inv'ention will be seen to have a light distribution curve which is substantially pear-shaped with a marked deformation of the upper portion of the pear-shape curve, and in fact such, that the pear-shaped curve has two inflections on either side of the axis of symmetry in the upper portion'of the pear-shaped curve, and that the pear configurationhas a bulge at its stalk. The report on the test received from the Lighting Engineering Laboratory reads as follows:

Object: Integral silvered grid, manufacturer Poul Willumsen. Scope of test: Measuring of photometric characteristics of optical grid.

A grid used below a lamp unit will, in addition to the transmission of light, also reflect the unit. The light reflected will travel back to the lamp unit and therefore 'to a certain extent hit the grid again and be transmitted.

matter of course be used for evaluating the useful effect of a real lamp unit. I

The light distribution curve of the incident flux on the grid has been drawn such that the maximum luminous power is equal to 10 divisions. Based on this determination of the scale ratio, the light distribution curves of the grids have been drawn.

RESULT OF MEASUREMENT The transmission factor of the grid is 55 percent. The distributions of light measured are attached in graphic form.

Naturally, a having the light distribution curve indicated, as stated in the body of the specification, could be designed in many ways. These embodiments are likewise comprised by the object of the invention as based on the disclosures of the present specification as they would be obvious'to one skilled in the art.

What I claim is:

1. A grid for fluorescent lamp units for ceiling or wall illumination, which comprises a system of equidistantly spaced open tubular elements having both external convex reflecting faces and internal concave reflecting faces, said faces being at least of single curvature and having a generant curve whose radius of curvature is constant or increasing in a direction away from a light source, the center of curvature of said generant curve of both faces being in a direction toward the interior of said tube, the end of said tubular elementfacing said light source having a smaller inner cross-sectional area than, the end away from Said light source, said grid being so constructed that the incident luminous flux 2. A grid according to claim 1, wherein said individual tubular elements are bodies of revolution.

3. A grid according to claim 1 wherein said generant curves are substantially parabolic segments, said generant curve of said external convex face conforming to said generant curve of said internal concave face.

4. A grid according to claim 3, wherein each said tubular element is a body of. revolution whose rotary axis forms a given angle (V) to the main axis (A) of a curve of the configuration y p x" of which said generant curve forms part thereof. I

5. A grid according to claim 4, wherein said curve of which said generant curve (P P of said body of revolution forms part is a second degree parabola (P), said rotary axis (C) forming a given angle (V) to the main axis (A).

6. A grid according to claim 5 wherein the focal point (B,) of said generant curve (P is proximate the edge of said body of revolution closest to said light source.

7. A grid according to claim 5 wherein said edge (B) of each tubular element farthest away from said light source is fixed relative to the geometric height (H) of the element by the light rays (L L originating from said edge (8,, B closest to said light source and having said given angle (V) to the axis of said element to cut off parabolic arches (P P at their points farthest away from said light source.

8. A grid according to claim 1, wherein said tubular elements have a cross section formed as a planar or spherical polygon with at least two sides.

9. A grid accordingto claim 8, wherein said convex and concave faces of the tubular elements have generant curves which are substantially parabolic segments (P.. 1

10. A grid according to claim 8, wherein said generant curve of the faces is a second degree parabola (P).

1 1. A grid according to claim 9, wherein a focal point of a face is located substantially at said edge of said element closest to said light source and opposite said respective face.

12. A grid according to claim 8, wherein said edge (B) of each said element farthest away from said light source is fixed relative to said geometric height (H) of the element, said light rays (L L originating from .said edge (B B closest to said light source and havmined luminous effect.

16. A' grid according to claim 15 wherein said individual tubular elements are interconnected such that their geometric center viewed from said light source and also from the opposite side of the grid towards said light source will form a plane polygonal or spheric polygonal pattern.

17. A grid according to claim 16, wherein said individual tubular elements are interconnected by a shielding grid having plane parallel walls at right angles to one another.

18. A grid according to claim 17, wherein said individual tubular elements are mounted with their rotary axis (A) coincident with an X-portion of said shielding grid.

19. A grid according to claim 17, wherein said individual tubular elements are mountedso as to have their rotary axis (A) coincide with the intersecting line of horizontal diagonals of individual openings of said shielding grid.

20. A grid according to claim 17, wherein said shielding grid is of lesser height than said individual tubular elements.

21. A grid according to claim 15 wherein said assembly defines spaces between said "elements, which are at least partly filled with opalescent material.

22. A grid according to claim 1 comprising a reflecting coating on said tubular elements.

23. A grid according to claim 22, comprising a coloring matter added to said reflecting coating of at least selected faces.

24. A grid according to claim 1 having light distribution curve in a polar coordinate system symmetrical about the 0 axis, extending as a closed curve below the axis with the latter as its horizontal tangent and having a humped portion just below the 90 axis, and being a substantially pear-shaped curve with a marked indentation in the upper portion of the pear-shaped curve, such that the pear-shaped curve has two inflections on either side of the axis of symmetry in the upper portion of the pearshaped curve.

25. A grid according to claim 1 having a light distribution curve shaped as a pear section having an enlarged extensionat its stalk.

26. A grid according to claim 24, wherein the proportions between the opening of said tubular elements and the opening therebetween are controlled to determine the proportions between the luminous flux transmitted in between said elements to thereby vary the size of said humped portion of said curve below the 90 axis. 

1. A grid for fluorescent lamp units for ceiling or wall illumination, which comprises a system of equidistantly spaced open tubular elements having both external convex reflecting faces and internal concave reflecting faces, said faces being at least of single curvature and having a generant curve whose radius of curvature is constant or increasing in a direction away from a light source, the center of curvature of said generant curve of both faces being in a direction toward the interior of said tube, the end of said tubular element facing said light source having a smaller inner cross-sectional area than the end away from said light source, said grid being so constructed that the incident luminous flux will be transmitted both through and in between said tubular elements.
 2. A grid according to claim 1, wherein said individual tubular elements are bodies of revolution.
 3. A grid according to claim 1 wherein said generant curves are substantially parabolic segments, said generant curve of said external convex face conforming to said generant curve of said internal concave face.
 4. A grid according to claim 3, wherein each said tubular element is a body of revolution whose rotary axis forms a given angle (V) to the main axis (A) of a curve of the configuration y p . xn of which said generant curve forms part thereof.
 5. A grid according to claim 4, wherein said curve of which said generant curve (P1, P2) of said body of revolution forms part is a second degree parabola (P), said rotary axis (C) forming a given angle (V) to the main axis (A).
 6. A grid according to claim 5 wherein the focal point (B1) of said generant curve (P1) is proximate the edge of said body of revolution closest to said light source.
 7. A grid according to claim 5 wherein said edge (B) of each tubular element farthest away from said light source is fixed relative to the geometric height (H) of the element by the light rays (L1, L2) originating from said edge (B1, B2) closest to said light source and having said given angle (V) to the axis of said element to cut off parabolic arches (P1, P2) at their points farthest away from said light source.
 8. A grid according to claim 1, wherein said tubular elements have a cross section formed as a planar or spherical polygon with at least two sides.
 9. A grid according to claim 8, wherein said convex and concave faces of the tubular elements have generant curves which are substantially parabolic segments (P1, P2).
 10. A grid according to claim 8, wherein said generant curve of the faces is a second degree parabola (P).
 11. A grid according to claim 9, wherein a focal point of a face is located substantially at said edge of said element closest to said light source and opposite said respective face.
 12. A grid according to claim 8, wherein said edge (B) of each said element farthest away from said light source is fixed relative to said geometric height (H) of the element, said light rays (L1, L2) originating from said edge (B1, B2) closest to said light source and having an inclination relative to said grid to cut off parabolic arches (P1, P2) at their points farthest away from said light source.
 13. A grid according to claim 1 made from a material capable of being formed into sheets.
 14. A grid according to claim 1 having a light distribution curve substantially formed as in FIG.
 11. 15. A grid according to claim 1 wherein said individual elements are so mounted with respect to each other so as to form a connected assembly having a determined luminous effect.
 16. A grid according to claim 15 wherein said individual tubular elements are interconnected such that their geometric center viewed from said light source and also from the opposite side of the grid towards said light source will form a plane polygonal or spheric polygonal pattern.
 17. A grid according to claim 16, wherein said individual tubular elements are interconnected by a shielding grid having plane parallel walls at right angles to one another.
 18. A grid according to claim 17, wherein said individual tubular elements are mounted with their rotary axis (A) coincident with an X-portion of said shielding grid.
 19. A grid according to claim 17, wherein said individual tubular elements are mounted so as to have their rotary axis (A) coincide with the intersecting line of horizontal diagonals of individual openings of said shielding grid.
 20. A grid according to claim 17, wherein said shielding grid is of lesser height than said individual tubular elements.
 21. A grid according to claim 15 wherein said assembly defines spaces between said elements which are at least partly filled with opalescent material.
 22. A grid according to claim 1 comprising a reflecting coating on said tubular elements.
 23. A grid according to claim 22, comprising a coloring matter added to said reflecting coating of at least selected faces.
 24. A grid according to claim 1 having light distribution curve in a polar coordinate system symmetrical about the 0* axis, extending as a closed curve below the 90* axis with the latter as its horizontal tangent and having a humped portion just below the 90* axis, and being a substantially pear-shaped curve with a marked indentation in the upper portion of the pear-shaped curve, such that the pear-shaped curve has two inflections on either side of the axis of symmetry in the upper portion of the pearshaped curve.
 25. A grid according to claim 1 having a light distribution curve shaped as a pear section having an enlarged extension at its stalk.
 26. A grid according to claim 24, wherein the proportions between the opening of said tubular elements and the opening therebetween are controlled to determine the proportions between the luminous flux transmitted in between said elements to thereby vary the size of said humped portion of said curve below the 90* axis. 